This invention relates to self-priming pump systems whereby a quantity of pumped liquid is permitted to flow to the suction side of a pump when suction has been lost, and more particularly to an improved valve structure which is operable in response to a loss of suction to automatically cause liquid to return to the suction side of the pump.
Self-priming liquid pumping systems are well known, and examples of systems of that type are illustrated in U.S. Pat. Nos. 3,370,604 and 3,381,618, each of which patents is commonly owned by the assignee of the present invention. As disclosed in those patents, a pump is positioned so that its suction inlet line is submerged in a suction chamber. The discharge line from the pump includes a downstream check valve to prevent reverse flow through the discharge line back to the pump when suction is lost. A priming valve is positioned between the pump discharge and the downstream check valve. The column of liquid between the priming valve and the check valve constitutes the priming liquid, and the flow of the priming liquid back to the suction chamber is controlled by the priming valve.
Heretofore the known priming valve structures included a pressure sensing device which extended into the liquid flow stream to sense the dynamic pressure thereof and to convey the same to the valve in order to operate the priming system, or it included a flow constriction in the form of a venturi in order to sense the reduced static pressure which results from the higher liquid flow velocity at the venturi throat, again to operate the priming valve. Such pressure sensors and venturis decreased the overall efficiency of the pumping system by impeding the flow therethrough.